Evaluating the solar inactivation of enveloped and non-enveloped bacteriophage using biological weighting functions in natural and simulated waters

• Biological weighting functions (BWFs) for two common human virus surrogates were determined • BWFs were leveraged to explore exogenous vs endogenous pathways in simulated and natural lake water • The endogenous inactivation rate for phi6 was 1.9 to 3.1 × faster than MS2 • Sensitizers enhanced inactivation for phi6, leading to 4 to 13 × faster inactivation • This study is the first to report a BWF for any enveloped virus or surrogate Sunlight plays a crucial role in regulating the persistence of human pathogens in contaminated water sources, yet a comprehensive understanding and comparison of its inactivation efficiency for both nonenveloped and enveloped viruses is lacking. The study presented herein determines the biological weighting function (BWF) for two bacteriophages commonly used as surrogates for human viruses, enveloped phi6 and nonenveloped MS2, using simulated sunlight and optical filters with a wavelength cutoff ranging between 280 and 395 nm. Inactivation experiments with varying concentrations (10, 20, 40 mg/L) of Suwannee River humic acid were conducted to understand the importance of the exogenous vs endogenous pathway. The endogenous inactivation rate of phi6 was found to be significantly faster than MS2, by a factor of 1.88 to 3.1 times, under simulated solar light with varying UVB content. The presence of humic acid greatly increased the inactivation rate through exogeneous mechanisms for both bacteriophages. This enhancement was particularly prominent for phi6, with inactivation rates 4 to 13 times higher. Laboratory studies were complemented with aquatic mesocosm experiments performed in a freshwater lake. Phi6 proved to be significantly more susceptible than MS2 to exogenous inactivation both in the laboratory and with natural lake water. This study is the first to report a BWF for any enveloped virus or surrogate. Results further elucidate the outsized heightened sensitivity of phi6 to exogenous inactivation, while the potential role of the envelope structure in the underlying mechanism is discussed.